As performance advantages in semiconductor devices are identified the speed of response in achieving these devices has been limited. Efforts have been undertaken to reduce the dimensions of the devices and to increase the carrier velocity so as to reduce the transit time of the careers and thereby improve the speed of response. With such efforts, however, have come difficulty in manufacture and serious restrictions on the impressed voltages.
One particularly high seed device was reported in Proceedings of the IRE Vol. 50, p. 1527, 1962. The device was composed of two Schottky barrier diodes back-to-back on a metal base. The device however was limited in that a long traverse time was required for the carriers to pass through the depletion layer in the emitter and also a long capacitive charging time was required for the emitter rectifying contacts.
As the art further developed, an improved structure appeared in the art as is described in copending patent application Ser. No. 118,171 (now abandoned) filed Feb. 4, 1980 wherein a two-stage emitter is provided, in which in the first stage there is a high density of carriers and the second stage which is adjacent to a high conductivity base there is a low barrier. The high conductivity base is of the order of the man free path of an electron.